1. Field of the Invention
This invention relates to a catalyst or catalyst component that is useful for polymerizing or copolymerizing alpha-olefins and more particularly concerns a magnesium-containing supported titanium halide-based catalyst or catalyst component for polymerizing or copolymerizing alpha-olefins in the slurry phase.
2. Discussion of the Prior Art
Hydrocarbon insoluble magnesium-containing supported titanium halide-based alpha-olefin polymerization or copolymerization catalyst components or catalyst systems containing such components are now well known in the art and are described, for example, in Hoppin et al., U.S. Pat. No. 4,829,038, which is incorporated in its entirety herein by reference. Typically, these catalyst components and catalyst systems are recognized for their performance based on activity and stereospecificity. However, commercial olefin polymerization or copolymerization, especially slurry-phase alpha-olefin polymerization or copolymerization, requires additional catalyst attributes for economical large-scale operation. Specifically, the production of relatively large particle size polymers or copolymers of an alpha-olefin in a commercial slurry phase polymerization or copolymerization of an alpha-olefin often results in difficulties in suspending and conveying the polymer or copolymer particles and in limited production rate and output and are attributed to the use of relatively large particle size catalysts in the polymerization or copolymerization process. Therefore, it is highly desirable to develop catalysts and catalyst components having reduced particle sizes for use in the polymerization or copolymerization of alpha-olefins in the slurry phase.
Disadvantages of efforts to reduce the particle size of such catalysts by catalyst attrition or comminution include the expenditure of additional time and effort and the production of catalyst particles having unpredictable, irreproducible and/or nonuniform sizes. In this regard, polymer or copolymer morphology is often critical and typically depends upon catalyst morphology, and good catalyst morphology generally involves uniformity of catalyst particle size. Consequently, it is very desirable to develop a method for making catalysts or catalyst components for use in the polymerization or copolymerization of alpha-olefins which have reproducible and predictable reduced particles sizes.
Numerous individual processes or process steps have been disclosed which have as their purpose the provision of improved supported, magnesium-containing, titanium-containing, electron donor-containing olefin polymerization or copolymerization catalysts. For example, the use of carbon dioxide in preparing a magnesium-containing support has been described in the aforementioned U.S. Pat. No. 4,540,679 as a means to improve control of the morphology of the catalyst and hence of the polymer product. Also, in a different context use of carbon dioxide was described in U.S. Pat. Nos. 4,246,383; 2,244,838; 4,529,715; and 4,530,915. Treating alcoholic solutions and suspensions of alkaline earth alcoholates with carbon dioxide or sulfur dioxide was noted in Chemical Abstracts, Vol. 76, 853050v (1972). Forming a soluble magnesium species has been described in U.S. Pat. Nos. 4,315,874; 4,399,054; 4,071,674; and 4,439,540. Examples of use of silicon compounds in formation of a catalyst component include U.S. Pat. Nos. 4,071,672; 4,085,276; 4,220,554; and 4,315,835. Tetrahydrofuran (THF) has been described variously to complex a magnesium chloride species (e.g., U.S. Pat. Nos. 4,482,687, 4,277,372, 3,642,746, and 3,642,772 and in European Patent No. 131,832); as modifier in a cocatalyst (e.g., U.S. Pat. Nos. 4,158,642 and 4,148,756); and as a solvent (e.g., U.S. Pat. Nos. 4,477,639 and 4,518,706). However the specific combination of steps taught in this invention to produce a catalyst with extremely advantageous properties has not been disclosed.
Arzoumanidis et al., aforesaid U.S. Pat. No. 4,866,022 discloses a method for forming a particularly advantageous alpha-olefin polymerization or copolymerization catalyst or catalyst component that involves a specific sequence of specific individual process steps such that the resulting catalyst or catalyst component has exceptionally high activity and stereospecificity combined with very good morphology. A solid hydrocarbon-insoluble, alpha-olefin polymerization or copolymerization catalyst or catalyst component with superior activity, stereospecificity and morphology characteristics is disclosed as comprising the product formed by 1) forming a solution of a magnesium-containing species from a magnesium hydrocarbyl carbonate or magnesium carboxylate; 2) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane; 3) reprecipitating such solid particles from a mixture containing a cyclic ether; and 4) treating the reprecipitated particles with a transition metal compound and an electron donor.
Arzoumanidis et al., aforesaid U.S. Pat. No. 4,540,679 disclose a process for the preparation of a magnesium hydrocarbyl carbonate by reacting a suspension of a magnesium alcoholate in an alcohol with carbon dioxide and reacting the magnesium hydrocarbyl carbonate with a transition metal component. Arzoumanidis et al., U.S. Pat. No. 4,612,299 disclose a process for the preparation of a magnesium carboxylate by reacting a solution of a hydrocarbyl magnesium compound with carbon dioxide to precipitate a magnesium carboxylate and reacting the magnesium carboxylate with a transition metal component.
Also known is incorporating an electron donor compound into the titanium-containing component as an internal modifier. An olefin polymerization system typically comprises a titanium-containing compound, an alkylaluminum compound and an electron donor external modifier compound. The electron donor external modifier used in combination with the alkyl aluminum compound and solid titanium-containing compound is distinct from the electron donor which may be incorporated as an internal modifier within the titanium-containing compound. Many classes of electron donors have been disclosed for possible use as electron donor external modifiers used during polymerization.
One class of such electron donor compounds is organosilanes. For example in U.S. Pat. No. 4,540,679, organosilanes, especially aromatic silanes, are described. Use of organosilanes as cocatalyst modifiers also is described in Published U.K. Application 2,111,066 and U.S. Pat. Nos. 4,442,276, 4,472,524, 4,478,660 and 4,522,930. Other aliphatic and aromatic silanes used in polymerization catalyst are described in U.S. Pat. Nos. 4,420,594, 4,525,555 and 4,565,798.
Hoppin et al., copending patent application Ser. No. 410,663, filed Sep. 21, 1989 and now Pat. No. 4,990,478, disclose specific branched C.sub.3 -C.sub.10 alkyl-t-butoxydimethoxysilanes modifiers which not only are used in supported catalysts to provide high yield and low atactic products, but which also produce a polymer with a broader molecular weight distribution than produced using the organosilane compound selected from the group consisting of diisobutyldimethoxysilane diisopropyldimethoxysilane, di-t-butyldimethoxysilane and t-butyl-trimethoxysilane, and mixtures thereof, as described in Hoppin et al., U.S. Pat. No. 4,829,038, which as indicated hereinabove, in its entirety is specifically incorporated by reference herein.
The aforesaid Arzoumanidis et al., U.S. Pat. No. 4,866,022 also discloses organosilanes that are useful as aforesaid internal modifiers in precipitating a solid from a soluble magnesium species and that have the formula R.sub.n SiR.sup.1.sub.4-n where n is 0 to 4, R is hydrogen or an alkyl, alkoxy, haloalkyl or aryl radical containing one to about ten carbon atoms or a halosilyl radical or haloalkylsilyl radical containing one to about eight carbon atoms, and R.sub.1 is OR or a halogen. The patent also discloses that aliphatic or aromatic silanes are advantageously employed as electron donor external modifiers and that preferred aliphatic silanes include isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, and t-butyltrimethoxysilane.
While each of the processes of the aforesaid U.S. Pat. Nos. 4,866,022; 4,540,679; and 4,612,299 affords alpha-olefin polymerization or copolymerization catalysts or catalyst components which have improved morphology and which afford polymer or copolymer products which also have improved morphology, it is highly desirable to develop alpha-olefin polymerization or copolymerization catalysts or catalyst components that have predictable and reproducible, reduced particle sizes and that afford polymers or copolymers that are more easily suspended and conveyed in the commercial polymerization or copolymerization of alpha-olefins in the slurry phase.